The present invention relates to an agricultural machine comprising an internal combustion engine, a particulate filter disposed in an exhaust-system branch of the internal combustion engine, and an engine control unit designed to prompt regeneration of the particulate filter as needed.
It is known per se to use particulate filters to capture soot particles emitted by a diesel engine during operation. Soot particles settle into capillaries of the filter, thereby causing the pressure drop at the filter to increase during operation; in the extreme case, the filter can become clogged. To prevent such clogging, the filter must be regenerated from time to time by burning off the soot particles deposited therein. The filter must be heated to a great extent in order to burn off the soot. A known approach therefor is to operate the engine at a no-load speed, i.e. with low air throughput, and to manipulate the fuel injection into the engine such that hot exhaust gasses are obtained. Such a manipulation can include, for example, delaying the point of injection of the fuel and increasing the quantity of fuel injected, or injecting the fuel in a plurality of thrusts per working cycle. The fuel that is injected in a delayed manner makes a minimal contribution to the drive power, and a large portion of the energy obtained from the combustion thereof leaves the engine in the form of hot exhaust gas which is used to bring the filter to regeneration temperature.
The heat output that reaches the filter in this manner must be coordinated exactly with the exhaust-gas throughput of the filter because the temperature range in which regeneration can take place is narrow. If the temperature is too low, the soot is not combusted; if the heat output that is supplied is too high, combustion can take place so rapidly that the heat released as a result damages the filter.
Operating at a no-load speed ensures that the exhaust-gas throughput is specified exactly and is limited to a low value, and so a relatively small quantity of fuel suffices to bring the exhaust gas to the required temperature. If the engine speed increases without the quantity of injected fuel being adapted, the exhaust-gas temperature decreases, the filter cools, and regeneration comes to a halt. A conventional engine control unit responds to this situation by aborting the regeneration. If regeneration is incomplete, soot becomes distributed unevenly in the filter. As a result, the quantity of soot in the filter can no longer be assessed reliably by reference to the pressure drop at the filter, and filter damage can occur if the engine is not automatically shut off in advance in a timely manner, because the pressure drop is concentrated at individual parts of the filter loaded heavily with soot, or because a locally thick soot layer releases so much heat in a subsequent regeneration process that the filter becomes damaged.
During practical application, the operator of such a conventional machine is therefore forced to interrupt the use of the machine every time the filter must be regenerated. Such a work interruption can result in considerable economic losses if it occurs at an unfavorable point in time. In particular, if a plurality of machines work together to perform a task, such as harvesting and hauling machines used to harvest a field, an interruption in the operation of one machine affects the other machines, thereby compounding the economic consequences.